in one sentence

why was Odysseus alone as the epic began

Odysseus was alone at the beginning of the epic because all of his companions had been killed or lost during their long and treacherous journey back from the Trojan War.

in one sentence

to whom was he telling his story? how did this person help him

Odysseus was telling his story to the Phaeacians, who ultimately helped him by providing him with transportation back to his homeland of Ithaca.

Odysseus was alone at the beginning of the epic because he had been separated from his crew after encountering various challenges and obstacles during his long journey back home from the Trojan War.